This invention relates in general to a method and apparatus for controlling the sequence of instructions in stored-program computers.
The sequence in which instructions are executed in stored-program computers may be changed by branch instructions. Aside from unconditional jumps, these branch instructions usually consist of two functions, viz. the verification of the presence of a specified condition and, if that condition is found, a transition to the next sequence instruction. This transition may consist of an incrementation of the instruction counter by two or n steps, instead of only one step (skip instruction), i.e., the next or the next n-1 instructions of the sequence are skipped. Alternatively, the transition may consist of a transfer of a new instruction address derived from the jump instruction to the instruction counter, after which the instruction sequence is carried on.
If both facilities for changing the instruction sequence are provided in a system, the skip instruction requires additional measures for changing the instruction address.
It is an object of the invention to provide means and method for simplifying the instruction sequence control and making it more flexible.